The purpose of this randomized and controlled study is to compare the effects of two ventilatory strategies during anesthesia induction of morbidly obese patients on both gas-exchange and functional residual capacity (FRC) modifications: 1- Control group: preoxygenation using 100% O2 via a face-mask and PEEP 10 cmH2O after intubation; 2- NIPPV group: preoxygenation using NIPPV and PEEP 10 cmH2O after intubation; 3- RM group: preoxygenation using 100% O2 via a face-mask and early RM plus PEEP 10 cmH2O after intubation.